The invention relates generally to the art of vapor generation and is particularly concerned with an improvement in an economizer system for cooperation with vapor generation apparatus such as a steam generator. An economizer is a heat exchanger located somewhere in the flue gas passage between the boiler and the stack. The economizer is designed to recover some of the waste heat from the products of combustion. Typically an economizer has a series of tubes through which water or other working fluid flows on its way to the boiler. The tubes typically are arranged in a chamber having an inlet connected to a boiler and an outlet connected to a stack. Such devices are intended to recover heat that would otherwise be wasted. It is a design consideration in economizers systems to limit the minimum temperature of the flue gases exiting the economizer. This may be desirable to prevent corrosion or to insure proper operation of the stack.
Existing technology to control the minimum temperature of flue gases leaving the economizer includes a flue gas bypass duct that is external to the main body of the economizer. A damper is provided in the external flue gas bypass duct to control the flow in the bypass duct. Flue gases flowing through the bypass duct are mixed with gases that flow directly through the economizer at a point downstream of the main body of the economizer. This bypass duct system is very costly and presents design problems because of thermal expansion as very hot flue gas pass through the duct and because there may be fatigue life concerns since the duct may rapidly change from relatively low temperatures to relatively high temperatures a large number of times during the life of the duct.
It is an object of the invention to provide an economizer system for vapor generation equipment that is more simple and less expensive to the manufacture.
Another object of the invention is to provide apparatus which eliminates design problems inherent in a bypass duct with respect to thermal expansion and fatigue life.
Still another object of the invention is to provide apparatus which will maximize the mixing of flue gases exiting the economizer.